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The Hubble Space Telescope Extragalactic Distance Scale Key Project. X. The Cepheid Distance to NGC 7331
The distance to NGC 7331 has been derived from Cepheid variablesobserved with the Hubble Space Telescope (HST) WFPC2, as part of theExtragalactic Distance Scale Key Project. Multiepoch exposures in F555W(~V) and F814W (~I), with photometry derived independently from DoPHOTand DAOPHOT/ALLFRAME programs, were used to detect a total of 13reliable Cepheids, with periods between 11 and 42 days. The relativedistance moduli between NGC 7331 and the LMC, derived from the V and Imagnitudes, imply an extinction to NGC 7331 of AV = 0.47 +/- 0.15 magand an extinction-corrected distance modulus to NGC 7331 of 30.89 +/-0.14 (random), equivalent to a distance of 15.1^{+1.0}_{-0.9} Mpc. Thereare additional systematic uncertainties in the distance modulus of+/-0.12 mag resulting from the calibration of the Cepheidperiod-luminosity relation and a systematic offset of +0.05 +/- 0.04 magif the metallicity correction inferred from the M101 results ofKennicutt et al. are applied.
| ISOCAM Mid-Infrared Imaging of the Quiescent Spiral Galaxy NGC 7331
Using the mid-infrared camera (ISOCAM) on the Infrared Space Observatory(ISO), the Sb LINER galaxy NGC 7331 has been imaged in two broadband andfour narrowband filters between 6.75 and 15 mu m. These maps show aprominent circumnuclear ring of radius 0.'25 x 0.'75 (1.1 x 3.3 kpc)encircling an extended central source. The 7.7 and 11.3 mu m dustemission features are strong in this galaxy, contributing approximatelyone-third of the total IRAS 12 mu m broadband flux. In contrast tostarburst galaxies, the 15 mu m continuum is weak in NGC 7331. Themid-infrared spectrum does not vary dramatically with position in thisquiescent galaxy, showing neither large-scale destruction of thecarriers of the emission bands nor a large increase in the 15 mu mcontinuum in the star-forming ring. In the bulge there is someenhancement of the LW2 (6.75 mu m) flux, probably because ofcontributions from photospheric light; however, the 11.3 mu m dustfeature is also seen, showing additional emission from interstellar orcircumstellar dust.
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